docs: def relations_for_id(relid=None):
      """Get relations of a specific relation ID"""
      relation_data = []
      relid = relid or relation_ids()
      for unit in related_units(relid):
          unit_data = relation_for_unit(unit, relid)
          unit_data['__relid__'] = relid
          relation_data.append(unit_data)
      return relation_data